1. Field of Invention
This invention relates in general to a parallel processing system, and in particular to virtual processors designed to allow multiple threads of work to execute concurrently with enhanced parallelism and availability.
2. Description of Related Art
Parallel processing systems are frequently comprised of an operating system and arrays of individual computers (i.e., processor nodes), each with their own central processing unit (CPU), memory, and data storage unit. Tasks are executed in parallel by utilizing each processor node.
During the execution of a task, a body of work is divided into multiple threads. A thread is a stream of instructions executed by the computer on behalf of a task. As an analogy, a task such as an orchestra performing a symphony can be decomposed into many threads which would be the individual musicians, each playing their part. Typically, in a parallel computer system, each thread is allocated to a different processor node. Each of these threads is then executed in parallel at their respective separate nodes. For instance, three threads can occupy and execute simultaneously on three different nodes at the same time. One of the advantages of this parallel processing technique is accelerated execution times. However, this technique should not be confused with the situation where one processor node executes a plurality of threads and the threads actually share or alternate slices of the processor node's total time.
Although the conventional form of parallel processing has merits, there are shortcomings. Conventional parallel processing techniques may result in an inefficient use of the available hardware. For example, if a processor node has multiple storage devices (i.e., disk drives) attached, then a single thread of execution might access only one of those devices at a time, leaving the other storage devices underutilized or even idle. In addition, if a parallel system is constructed out of multiprocessor nodes, then a single thread per node might not utilize all of the available CPUs in the node.